The objective of the proposed program is to study etiologic factors and pathogenetic mechanisms in renal disease in childhood and to explore factors involved in renal allograft rejection. In addition to studying patients, appropriate models will be investigated. The specific aims are as follows: (1) to attempt to identify antigens in glomeruli in disease presumed to have an immune complex pathogenesis, (2) to study factors responsible for the localization of circulating immune complexes in glomeruli, (3) to investigate the ultrastructural basis for increased glomerular permeability in experimental immunologically induced glomerular disease, (4) to study the nature of the mononuclear cells participating in certain cell-mediated reactions, (5) to investigate abnormalities of the complement system in renal disease, (6) to explore mechanisms of immunological tolerance, (7) to study the immunosuppressive properties of anti-lymphocyte serum and the immunological reactivity of renal allograft recipients, and (8) to study the synthesis of the first component of complement by epithelial cells of bladder, ureters, and renal pelvis.